1. Field of the Invention
The present invention relates to an optical inspecting apparatus, and more specifically, to a three-dimensional profile inspecting apparatus.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Accurate profile inspection is an important modern technology. With recent downsizing of many devices, accurate and reliable inspection technology is needed to measure dimensions and profiles of miniature structures so as to control quality and process. An optical non-contact detection technology capable of obtaining exact profile information of a subject in a non-destructive manner is required for a wide variety of applications.
Referring to FIG. 1, the objective lens used by a typical microscope 11 is frequently of a magnification ratio less than 20, and thus has a small aperture. Consequently, if the slope of a profile surface of a subject 12 to be inspected is large, the reflection light 13 from the subject 12 cannot enter the microscope 11, so the profile image of the subject 12 cannot be obtained. As a result, some profile information for the subject must be estimated by numeral interpolation, and the actual profile, dimension and roughness data cannot be acquired.
Taiwan Pat. No. 1229186 uses a linear scanning apparatus with dual view angles equipped with an inclined light source to detect approximate shapes and dimensions of a defect. The main advantages of such design include the capability to quickly inspect large areas and judge whether the defect is a protrusion or a recess. However, the apparatus cannot precisely measure the three-dimensional profile of a miniature structure, and cannot resolve the problem of difficulty in capturing the surface signal if the slope of the profile of the subject is large.
U.S. Pat. No. 6,449,048 uses an interferometer to scan the sample surface laterally with respect to the optical axis of the interferometer objective at a tilt angle, which allows the sample surface not exceed the maximum coherence plane of the interferometer. Thereby, a traditional vertical scanning interferometer (VSI) can be used to laterally scan the surface of the subject and the profile of the subject can be obtained without using image stitching technology. However, due to the limitation of the angle of the maximum coherence plane for the chosen objective, this method also cannot resolve the problem where the profile cannot be captured if the slope of the sample surface is larger than the angle of the maximum coherence plane of the interferometer. Furthermore, according to the nature of the lateral scanning at single axis, the profile of the sample surface should all be located within the maximum coherence plane along the longitudinal direction with respect to the optical axis of the interferometer objective, otherwise the complete profile cannot be obtained completely.
QED Technology™ developed a method of tilting and rotating the subject to obtain the profile of a subject with a large surface of a large slope. However, this method is restricted to the applications with small subjects, and cannot be used for large subjects that cannot be tilted.